Thyroid Function in Late Preterm Infants

Transient hypothyroxinemia (TH) is a condition characterized by low levels of serum thyroxine (T4) and normal levels of thyroid stimulating hormone (TSH). TH in premature infants has been found to be related to severity of illness. T4 levels in very low birth weight infants born prematurely has been found to be inversely correlated to severity of illness. In very low birth weight infants, TH has been associated with poor outcomes. Little is known about thyroid function in late preterm infants. Hypotheses: 1. Ill late preterm infants will have lower total T4 levels than healthy late preterm infants. 2. Total T4 and possibly TSH levels will be inversely correlated with short-term outcomes. 3. Late Preterm infants born by cesarean section will have lower T4 levels compared to those born by vaginal birth.